I either use decapitation or blunt trauma depending on the fish.
Fish like Cichlids and big catfish or other wide bodied fish i place in a damp towel with just their heads protruding, place the head of the fish onto a wooden baord, take a deep breath and smack them cleanly on the head with a 20 ounce hammer. Death is instant.
For slim bodied fish like eels or bichirs i again wrap them in a towel with just the head protruding, place them on a wooden board but instead of a hammer i remove their head with one motion using a chefs cleaver. Again death is instant.
Fish like Cichlids and big catfish or other wide bodied fish i place in a damp towel with just their heads protruding, place the head of the fish onto a wooden baord, take a deep breath and smack them cleanly on the head with a 20 ounce hammer. Death is instant.
For slim bodied fish like eels or bichirs i again wrap them in a towel with just the head protruding, place them on a wooden board but instead of a hammer i remove their head with one motion using a chefs cleaver. Again death is instant.